I think you will find Mississauga is a bit too far. When you said centre of Toronto, do you mean Midtown or downtown Toronto?

You may find Etobicoke, near Bloor and Islington area, alone the Subway line (Underground) is quite family oriented, walking distance to parks, shops and restaurants, especially subway Station. But real estate is not cheap, more than CAD$500K.

If you have kids who are going to school, North York has many good schools. Again, look for places along the subway line, like Yonge/Finch, Yonge/York Mills, Yonge/North York Centre...